Novel photographic product,process and composition



3,459,580 NOVEL PHOTOGRAPHIC PRODUCT, PROCESS AND COMPOSITION Howard C. Haas, Arlington, Mass, assignor to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware No Drawing. Filed Sept. 26, 1966, Ser. No. 581,754 Int. Cl. G03c 11/08 US. Cl. 117-34 4 Claims This invention relates to a composition of matter comprising a novel mixture of materials and to the process of washing and protecting a photographic silver print by applying to its image-carrying face, in a layer, an aqueous solution of materials capable of producing a protective coating when the composition is dried.

It has been proposed, in order to improve the stability of a photographic image prepared by a diffusion-transfer process, to coat the image with a composition comprising an aqueous solution of a film-forming material. The water acts to wash traces of photographic reagents from the image and to so distribute the film-forming material that it provides the image with a smooth protective coating when it is dried. Processes of the foregoing type are described in United States Patent No. 2,719,791, issued on Oct. 4, 1955.

A primary object of the present invention is, therefore, to provide a process for increasing the stability of a developed photographic silver image by applying an aqueous solution of materials capable of forming a protective coating upon the image when the composition is dried.

Another object is to provide, as a novel product, a protected photographic image produced by the above process.

An additional object is to provide, for use in a process of the foregoing type, a composition comprising a mixture of a vinylpyridine polymer and a quaternary salt of polyvinyl pyridine, the preferred salt being the methyl-ptoluene sulfonate quaternary salt of poly-2-vinylpyridine, hereinafter referred to as poly-N-methyl-Z-vinyl pyridinium tosylate,

A further object is to provide for use in a process of the foregoing type, a composition containing the above constituents in combination with a salt of a heavy metal which forms an insoluble sulfide.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps and the relation and order of one or more of such steps with respect to each of the others, and the composition and product possessing the features, properties and relation of elements which are exemplified in the following detailed disclosure, and the scope of the application which will be indicated in the appended claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

The process of the present invention is particularly useful for washing and protecting photographic silver images prepared in accordance with well-known diffusion- Sta-1m atent Othce 3,459,580 Patented Aug. 5, 1969 transfer processes, for example, as described in United States Patent No. 2,719,791, issued to Edwin H. Land on Oct. 4, 1955.

A photographic silver image of the foregoing type ordinarily may retain traces of the developing reagents with which it has been processed, the continued presence of which may adversely affect the stability of the resultant image. For example, silver may be oxidized by sulfur from the residue of sodium thiosulfate, which has been employed as a silver solvent, or the silver may be oxidized by numerous oxidizing agents present in the atmosphere. Additionally, the image may contain traces of silver ion in equilibrium with metallic silver, so that in areas where the image is subjected to materials which form insoluble silver residues, such as sulfides, these residues react with the silver ion, causing more metallic silver to shift to the ionic state, ultimately undesirably affecting image silver. Furthermore, traces of unoxidized developer, if oxidized by atmospheric oxygen, may discolor the highlights of the image.

The compositions of matter contemplated by the present invention generally comprise mixtures of compatible components which, when mixed together, possess properties not possessed by the components themselves. A typical mixture of such components is an aqueous solution of a vinylpyridine polymer and a quaternary salt of of polyvinyl pyridine.

It may also be desirable to add an amount of another polymeric material to the coating composition to further enhance its protective properties. The preferred material for this purpose is a hydantoin formaldehyde condensation polymer, such as that described in United States Patent No. 2,874,045, issued Feb. 17, 1959, to Edwin H. Land.

The addition to the coating composition of a salt of a heavy metal which forms insoluble sulfides is found to still further enhance the impermeability of the resultant coating to attack by compounds containing sulfur, and as such is considered to be a desirable additive.

A water-miscible organic solvent and an acid, preferably a weak acid, are also found to produce additional beneficial results when added to the coating composition. It is believed that they play an important function in facilitating the solution of the vinylpyridine polymer.

The vinylpyridine polymer alone, or in combination with a hydantoin formaldehyde condensation polymer, functions primarily to impart to the dried print-coating composition substantial impermeability to elemental sulfur, stability throughout wide temperature and humidity ranges, resistance to the effects of prolonged solar radiation, and optical clarity.

The heavy metal salt functions primarily to impart to the composition excellent resistance to penetration by sulfides; for example, those present in the atmosphere.

It has been unexpectedly found that if a quaternary salt of polyvinyl pyridine, such as poly-N-methyl-2Fvinyl pyridinium tosylate, is added to a polyvinyl pyridine print-coating composition, the resultant protective coating on the print displays vastly improved adhesion to the silver image, increased stability against cracking and flaking, and reduced tackiness. Accordingly, this invention is particularly directed to a process for washing and protecting a photographic silver image, and to a polymeric composition for use in that process, said composition containing as a necessary ingredient a quaternary salt of polyvinyl pyridine.

In accordance with the present invention a preferred composition for this purpose comprises as aqueous solution containing: (1) a vinylpyridine polymer, (2) a hydantoin formaldehyde condensation polymer, (3) a salt of a heavy metal which forms an insolube sulfide, (4) a water-miscible organic solvent, (5) a weak acid, and (6) a quaternary salt of polyvinyl pyridine. This solution, because of its aqueous character, is readily adapted to remove residual water-soluble photographic processing reagents from intimate contact with the photographic image.

The vinylpyridine polymer utilized in the instant invention may be a polyvinyl pyridine such as poly-2-vinylpyridine, poly-3-vinylpyridine, poly-4-vinylpyridine, poly- 2-vinyl-6-methyl pyridine, poly-2-methyl-5-vinylpyridine, poly-2-vinyl-5-ethyl pyridine, or a copolymer in which a vinylpyridine is the characteristic ingredient, such as a copolymer of 2-vinylpyridine and methylacrylate, 2- vinylpyridine and methyl methacrylate, 2-vinyl-pyridine and methylvinyl ketone, 2-vinylpyridine and acrylamide, etc. The preparation of such vinylpyridine polymers is illustrated in United States Patent No. 2,491,472, issued in the name of J. Harmon on Dec. 20, 1949, for Polymerization of Vinyl Pyridines. The use of such vinylpyridine polymers is illustrated in United States Patent No. 2,830,900, issued to Edwin H. Land et al. on April 15, 1958.

The coating formed when the print-coating composition is applied to a silver image and dried displays increased stability to cracking and flaking due to the quaternary salt of polyvinyl pyridine which increases the adhesion of the vinylpyridine and hydantoin formaldehyde condensation polymer to the photographic image. It has further been found that whereas a vinylpyridine polymer alone yellows under intense light, a mixture of a vinylpyridine polymer and a hydantoin formaldehyde condensation polymer retains its optical clarity under prolonged exposure to light. Furthermore, it has been found that hydantoin formaldehyde condensation polymers, if included in polyvinyl pyridine print-coating compositions, render the resultant dry coating less pervious to elemental sulfur, which may originate in sulfur-containing papers or cardboards that come into contact with the coating during ordinary use or storage of photographic prints. A preferred hydantoin formaldehyde condensation polymer is dimethyl hydantoin formaldehyde.

The preferred composition contains a concentration of a salt of a heavy metal, which is capable of forming an insoluble sulfide, which is large relative to the quantity of silver in the image. Consequently, in accordance with the law of mass action, atmospheric sulfides which penetrate the coating react with the heavy metal salt in preference to the silver of the image. Preferably, the concentration of the heavy metal salt, by total weight of the preferred composition, ranges approximately from 1% to 15%. The heavy metal salt, preferably water soluble, contains a heavy metal cation such as cadmium, lead, manganese, zirconium, zinc, or tin; and an anion such as acetate, sulfate, nitrate or formate. The quantity of salt, although large relative to the quantity of silver in the image, should be so small that the salt and its sulfide do not appreciably affect the appearance of the image. Heavy metal salts which are pale in appearance and which react to form pale sulfides under atmospheric conditions are preferred. The salts of zinc, in particular, are preferred because they and their sulfides are white.

Organic solvents and weak acids have been found to cooperate to facilitate the formation of the solution of the vinylpyridine polymer, which ordinarily possesses a relatively low degree of solubility in water. It is believed that salt formation by a portion of the acid and a portion of the basic groups of the polymer is one of the drivmg forces for enhancing solubility of the polymer in water. The water-miscible organic solvent, when rapidly 'vaporizable, functions additionally to impart to the solution an overall quick-drying character. Examples of appropriate organic solvents are: low molecular weight alcohols, such as methanol, ethanol, isopropanol, etc.;

dioxane; and low molecular weight ketones, such as acetone, methylethyl ketone, etc. Examples of appropriate weak acids are: acetic acid; propionic acid; etc.

The preferred composition is prepared by dissolving the vinylpyridine polymer in a mixture of water, organic solvent and acid at a temperature ranging from room temperature to 40 C. under a reflux condenser to prevent evaporation of the alcohol. A hydantoin formaldehyde condensation polymer may be then added. Thereafter, the quaternary salt of polyvinyl pyridine and the heavy metal salt may be stirred into the mixture. A suitable preferred composition comprises the foregoing ingredients in the following proportions:

Poly-2-vinylpyridine grns 8-35 Hydantoin formaldehyde condensation polymer gms 0-5 Salt of heavy metal having insoluble sulfide cgmsu l-lO Poly N methyl 2 vinyl pyridinium tosylate -gms 1.0-4.5 Water ml 50-85 Organic solvent ml 20-50 Weak acid ml 0-20 The poly-N-methyl-Z-vinyl pyridinium tosylate can be made by treating a solution of poly-2-vinylpyridine in ethanol with a 1.5 molar excess of methyl-p-toluene sulfonate. The mixture is refluxed for several hours and precipitated in diethyl ether with constant stirring. The resultant poly-N-rnethyl-Z-vinyl pyridinium tosylate is filtered, washed with ether and dried. Other methods are described in United States Patent No. 2,484,430.

Examples of photographic materials useful in the production of the photographic silver images to which the preferred composition may be most advantageously applied are described in detail in Patent No. 2,543,181, issued in the name of Edwin H. Land on Feb. 27, 1941; in Patent No. 2,647,056, issued in the name of Edwin H. Land on July 28, 1953; and in application of Edwin H. Land, Ser. No. 293,326, filed July 8, 1963, now Patent No. 3,351,466.

Preferably the composition of the present invention is applied to a photographic silver image by means of an absorbent applicator composed, for example, of flannel, cotton batting, or cellulose sponge charged with the composition. When the image is swabbed with such an applicator, residual reagents in the image are dissolved and, for the most part, transferred into the applicator, and the image becomes coated with a thin layer of the dispersion. The solution can then be dried to form a coating over the image.

The composition referred to above, after being swabbed by means of such an absorbent applicator onto a photographic silver image of the above-described nature, rapidly dries under ordinary atmospheric conditions to form a coating over the image which has excellent protective properties.

The following example is given for illustration and is not intended to limit the scope of the instant invention.

Example A composition for washing and protecting a photographic silver image was prepared by combining and blending the following materials to provide a uniform solution:

Poly-2-vinylpyridine gms 13.5 Dimethyl hydantoin formaldehyde condensation polymer gms 2.2 Poly-N-methyl-Z-vinyl pyridinium tosylate gms". 1.5 Zinc acetate dihydrate gms 4.5 Water ml 70 Isopropanol ml 30 Acetic acid (glacial) ml 4.5

Photographic silver transfer images were prepared by exposing photosensitive silver halide elements to a stepwedge; developing the resulting latent images by spreading between the exposed photosensitive elements and superposed image-receiving elements a processing composition containing a viscous aqueous solution of a silver halide developing agent, a silver halide solvent, and an alkali; maintaining the respective elements in superposed relation for approximately one minute, during which undeveloped silver halide forms a soluble silver complex which diffuses through the layer of composition to the image-receiving elements where, upon being reduced to silver, it forms a silver print; and stripping the photosensitive elements, together with the layer of composition, from the respective image-receptive elements. The film units so employed were translucent base X-ray diffusion-transfer film units.

The photographic silver images so prepared were swabbed by means of an absorbent applicator with the above solution. The photographic prints so treated dried rapidly under ordinary atmospheric conditions, after which they were subjected to the following tests:

(a) The prints were allowed to remain in closed chambers at a temperature of 100 F. and 80% relative humidity for a period of about 40 hours.

(b) The prints were suspended over water at 100 F. for a period of about ten days.

(c) The prints were subjected to the ASA standard method for determining brittleness, PH 132-1958, by which resistance to cracking and flaking was evaluated.

((1) The prints were subjected to 4 and 8 hour periods in an atmosphere containing hydrogen sulfide at room temperature.

(e) The prints were stacked face-to-face at room temperature and humidity; a weight was placed on the stack.

After all of the foregoing tests, it was observed that in none of the prints was there any deterioration of the silver image, nor was there any loss in the density of the light steps of the image. The prints were exceptionally non-tacky, as evidenced by their failure to adhere to one another in test (e) above. Moreover, there was little or no image discoloration in any of the prints, and coatings on the prints used in (c), above, demonstrated unusual stability against cracking and flaking.

Since certain changes may be made in the above process, composition and product without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A process for Washing and protecting a diffusiontransfer photographic silver print which includes the steps of: (1) applying to the image-carrying face thereof a layer of an aqueous composition comprising a mixture of a vinylpyridine polymer and a quaternary salt of a vinylpyridine polymer; and (2) drying said layer.

2. The process of claim 1 wherein said quaternary salt is poly-N-methyl-Z-vinyl pyridinium tosylate.

3. The process of claim 2 wherein said vinylpyridine polymer is poly-2-vinylpyridine.

4. The process of claim 1 wherein said aqueous composition comprises poly-2-vinylpyridine, poly-N-methyl-2- vinyl pyridinium tosylate, dimethyl hydantoin formaldehyde, acetic acid, isopropanol, and zinc acetate dihydrate.

References Cited UNITED STATES PATENTS 2,612,446 7/ 1952 Umberger -a 260-296 2,874,045 2/1959 Land 9629 2,979,477 5/1958 Land 260-294 3,007,228 11/1961 Matsubayaski et al. 260-29.6 3,161,506 11/1964 Becker 9676 NORMAN G. TORCHIN, Primary Examiner I. P. BRAMMER, Assistant Examiner US. Cl. X.R. 9649 

1. A PROCESS FOR WASHING AND PROTECTING A DIFFUSIONTRANSFER PHOTOGRAPHIC SILVER PRINT WHICH INCLUDES THE STEPS OF: (1) APPLYING TO THE IMAGE-CARRYING FACE THEREOF A LAYER OF AN AQUEOUS COMPOSITION COMPRISING A MIXTURE OF A VINYLPYRIDINE POLYMER AND A QUATERNARY SALT OF A VINYLPYRIDINE POLYMER; AND (2) DRYING SAID LAYER. 